Mathematics

Mathematics

Problem

Given sec⁡β=−135\sec\beta=-\dfrac{13}{5} and π<β<3π2\pi<\beta<\tfrac{3\pi}{2}, compute the exact value of sin⁡βcos⁡β+tan⁡2β\sin\beta\cos\beta + \tan^{2}\beta.
Intuitive explanation

You're working with a secant value in the third quadrant, where both sine and cosine are negative. The key is to use the reciprocal relationship cos⁡β=1sec⁡β\cos\beta = \frac{1}{\sec\beta} to find cos⁡β\cos\beta, then the Pythagorean identity to find sin⁡β\sin\beta. Once you have both, the expression breaks into two manageable pieces: a product sin⁡βcos⁡β\sin\beta\cos\beta and a ratio squared tan⁡2β=sin⁡2βcos⁡2β\tan^2\beta = \frac{\sin^2\beta}{\cos^2\beta}.

Intuitive explanation

You're working with a secant value in the third quadrant, where both sine and cosine are negative. The key is to use the reciprocal relationship cos⁡β=1sec⁡β\cos\beta = \frac{1}{\sec\beta} to find cos⁡β\cos\beta, then the Pythagorean identity to find sin⁡β\sin\beta. Once you have both, the expression breaks into two manageable pieces: a product sin⁡βcos⁡β\sin\beta\cos\beta and a ratio squared tan⁡2β=sin⁡2βcos⁡2β\tan^2\beta = \frac{\sin^2\beta}{\cos^2\beta}.

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